index.js

// Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

//     push(x)-- Push element x onto stack.
//         pop()-- Removes the element on top of the stack.
//             top()-- Get the top element.
//                 getMin()-- Retrieve the minimum element in the stack.

// Example 1:

// Input
// ["MinStack", "push", "push", "push", "getMin", "pop", "top", "getMin"]
// [[], [-2], [0], [-3], [], [], [], []]

// Output
// [null, null, null, null, -3, null, 0, -2]

// Explanation
// MinStack minStack = new MinStack();
// minStack.push(-2);
// minStack.push(0);
// minStack.push(-3);
// minStack.getMin(); // return -3
// minStack.pop();
// minStack.top();    // return 0
// minStack.getMin(); // return -2

// Constraints:

// Methods pop, top and getMin operations will always be called on non - empty stacks.

// Solution

class MinStack {
  constructor() {
    this.stack = [];
    this.min = Infinity;
  }
}

MinStack.prototype.push = function (x) {
  this.stack.push(x);
  this.min = Math.min(this.min, x);
};

MinStack.prototype.pop = function () {
  this.stack.pop();
  this.min = Math.min(...this.stack);
};

MinStack.prototype.top = function () {
  return this.stack[this.stack.length - 1];
};

MinStack.prototype.getMin = function () {
  return this.min;
};